1. Field of the Invention
The present invention relates to a multiplex transmission apparatus which has a plurality of communication nodes connected via a multiplex bus, and outputs an operation command signal from a communication node connected to an input switch to another communication node connected to an electrical component via the multiplex bus.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Patent Laid-Open No. 1-143535, a multiplex transmission system has been proposed. In this system, a plurality of communication nodes equipped in, e.g., a vehicle are connected in a network pattern using a common multiplex bus, and the multiplex bus is shared by a plurality of electrical components, thereby simplifying the harness structure for connecting the electrical components and input switches for operating these members.
The multiplex transmission system includes communication nodes which are set in a sleep state, i.e., an inoperative state when an ignition switch is turned off, and communication nodes which are set in a wake-up state, i.e., an operable state by a battery power supply even when the ignition key is not ON. Communication nodes for controlling electrical components such as door lock switches, head lamps, and the like, which must operate when the ignition switch is in an OFF state are maintained in the wake-up state by electrical power supplied from the battery power supply, thereby allowing operations of these electrical components.
When the communication nodes which are to be set in the wake-up state by the battery power supply are always maintained in the wake-up state, a dark current flows to waste battery power. For this reason, these communication nodes are designed to shift to the sleep state when the door locks are locked in the OFF state of the ignition switch, and to shift back to the wake-up state when a driver touches a door handle later.
In the conventional system with the above arrangement, when a person other than a driver accidentally touches a door handle, the communication nodes which are set in the wake-up state by the battery power supply shift from the sleep state to the wake-up state, thus wasting battery power. When a time interval from when the driver touches the door handle and the communication nodes shift to the wake-up state until required input switches are actually operated is long, a dark current which flows during this interval is wasted. On the contrary, when the above-mentioned time interval is short, an operation command signal of an electrical component is output before the communication nodes shift to the wake-up state, and this electrical component cannot often be properly operated.
For this reason, it is desired that when a driver performs a switch operation for operating an electrical component, the corresponding communication node is shifted to the wake-up state in response to this switch operation, and the electrical component corresponding to the operated switch can be quickly operated.